Egidio Astesiano Gianna Reggio An Attempt at Analysing the Consistency Problems in the UML from a Classical Algebraic Viewpoint. 56-81 http://dx.doi.org/10.1007/978-3-540-40020-2_3 2002 conf/wadt/2002 WADT db/conf/wadt/wadt2002.html#AstesianoR02